Stiffened skin composite panels are frequently used to replace composite skin, honeycomb sandwich panels used for fairings and close-out panels on aircraft or other lightweight structures. One problem with using a stiffened skin composite panel to replace a sandwich panel is weight. In a conventional method of manufacturing a stiffened skin composite panel, structural foam is used as a mandrel over which stiffeners are laminated. The foam mandrel generally remains in place in the finished panel. Inclusion of the foam mandrel results in overall panel weight that exceeds that of a comparable performance sandwich panel. This increased weight is generally intolerable.
One alternative conventional approach to manufacturing a stiffened skin composite panel which results in hollow stiffeners is to produce a tool on which the skin portion of the panel is laminated and another tool on which the stiffener portion of the panel is fabricated. Such tools are expensive and this option for manufacturing is often not economically feasible. Another problem with this approach is the fit between the components after they are fabricated on separate tools. Raw material variability also exacerbates the problems in a production setting. These problems tend to eliminate a stiffened skin composite panel concept in many instances.
Another general problem with composite skin sandwich panel fairings is the eventual accumulation of moisture in the honeycomb cells. The moisture degrades the structural performance of the panels as well as increases the weight of the assembly. Hollow stiffeners with drain holes prevent the accumulation of moisture and all of the associated problems.
The present invention is directed to overcoming one or more of the problems discussed above, in a novel and simple manner.